In our study, we first reported the hypomethylation of HLA-DRB1 in psoriatic epidermis; more importantly, our data proved that methylation of HLA-DRB1 is negatively correlated with the severity of the disease, suggesting that the methylation status of HLA-DRB1 can become a potential bio-marker for the diagnosis or evaluating the efficacy of treatment of psoriasis. The gene discussed is HLA-DRB1; the disease is psoriasis.